Hajo,
I think it’s ok for me from low C to E (top staff), passively and very soft sound. But when I have to activate for a louder sound (not FFF) and/or to play higher, I don’t understand how to do with coners, aperture and top lip (bottom lip is ok with milk spout).
Is the first goal is to have soft sounds, for each note, “only” with corners, then second step : to play with a louder sound, comes with work ?

Regards
Jérôme